Re: [PATCH v5 0/7] dma-buf: Performance improvements for system heap & a system-uncached implementation

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Nov 12, 2020 at 08:11:02PM -0800, John Stultz wrote:
> On Thu, Nov 12, 2020 at 1:32 AM Daniel Vetter <daniel@ffwll.ch> wrote:
> > On Thu, Nov 12, 2020 at 11:09:04AM +0530, Sumit Semwal wrote:
> > > On Tue, 10 Nov 2020 at 09:19, John Stultz <john.stultz@linaro.org> wrote:
> > > >
> > > > Hey All,
> > > >   So just wanted to send my last revision of my patch series
> > > > of performance optimizations to the dma-buf system heap.
> > >
> > > Thanks very much for your patches - I think the first 5 patches look good to me.
> > >
> > > I know there was a bit of discussion over adding a new system-uncached
> > > heap v/s using a flag to identify that; I think I prefer the separate
> > > heap idea, but lets ask one last time if any one else has any real
> > > objections to it.
> > >
> > > Daniel, Christian: any comments from your side on this?
> >
> > I do wonder a bit where the userspace stack for this all is, since tuning
> > allocators without a full stack is fairly pointless. dma-buf heaps is a
> > bit in a limbo situation here it feels like.
> 
> As mentioned in the system-uncached patch:
> Pending opensource users of this code include:
> * AOSP HiKey960 gralloc:
>   - https://android-review.googlesource.com/c/device/linaro/hikey/+/1399519
>   - Visibly improves performance over the system heap
> * AOSP Codec2 (possibly, needs more review):
>   - https://android-review.googlesource.com/c/platform/frameworks/av/+/1360640/17/media/codec2/vndk/C2DmaBufAllocator.cpp#325
> 
> Additionally both the HiKey, HiKey960 grallocs  and Codec2 are already
> able to use the current dmabuf heaps instead of ION.
> 
> So I'm not sure what you mean by limbo, other than it being in a
> transition state where the interface is upstream and we're working on
> moving vendors to it from ION (which is staged to be dropped in 5.11).
> Part of that work is making sure we don't regress the performance
> expectations.

The mesa thing below, since if we test this with some downstream kernel
drivers or at least non-mesa userspace I'm somewhat worried we're just
creating a nice split world between the android gfx world and the
mesa/linux desktop gfx world.

But then that's kinda how android rolls, so *shrug*

> > Plus I'm vary of anything related to leaking this kind of stuff beyond the
> > dma-api because dma api maintainers don't like us doing that. But
> > personally no concern on that front really, gpus need this. It's just that
> > we do need solid justification I think if we land this. Hence back to
> > first point.
> >
> > Ideally first point comes in the form of benchmarking on android together
> > with a mesa driver (or mesa + some v4l driver or whatever it takes to
> > actually show the benefits, I have no idea).
> 
> Tying it with mesa is a little tough as the grallocs for mesa devices
> usually use gbm (gralloc.gbm or gralloc.minigbm). Swapping the
> allocation path for dmabuf heaps there gets a little complex as last I
> tried that (when trying to get HiKey working with Lima graphics, as
> gbm wouldn't allocate the contiguous buffers required by the display),
> I ran into issues with the drm_hwcomposer and mesa expecting the gbm
> private handle metadata in the buffer when it was passed in.
> 
> But I might take a look at it again. I got a bit lost digging through
> the mesa gbm allocation paths last time.
> 
> I'll also try to see if I can find a benchmark for the codec2 code
> (using dmabuf heaps with and without the uncached heap) on on db845c
> (w/ mesa), as that is already working and I suspect that might be
> close to what you're looking for.

tbh I think trying to push for this long term is the best we can hope for.

Media is also a lot more *meh* since it's deeply fragmented and a lot less
of it upstream than on the gles/display side.

I think confirming that this at least doesn't horrible blow up on a
gralloc/gbm+mesa stack would be useful I think.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch